Partial purification and characterization of an inducible extracellular β-Glucosidase of <i>Aspergillus niger</i> IMI 502691

Abstract

β-Glucosidase (EC 3.2.1.21) was produced by Aspergillus niger IMI 502691 using solid state fermentation of cassava root fibre. The enzyme was partially purified and characterized. The enzyme extracted using 20mM phosphate buffer pH 6.8 was concentrated to 10ml with 5M sucrose solution using dialysis membrane. It was purified from the culture medium by ion exchange chromatography on Carboxymethyl Sepharose and gel filtration chromatography on Biogel P 4. β- Glucosidase was purified 3.17 fold to give 3.68% yield relative to the total activity in the crude extract and with over 300% increase in specific activity of 106.93Umg^-1 proteins for the partially purified protein. The enzyme exhibited decrease in total protein and total activity of 86.1% and 27.16%, respectively and optimal activity at pH 5.0 and 80^oC (1h) in the absence of calcium. The β- glucosidase showed a wide range of pH and temperature of 3.0 to 7.0 and 50^oC to 90^oC, respectively. The enzyme was most stable at 50^oC but retained above 50% of its activity for 1h at 60^oC. The β-glucosidase of Aspergillus niger IMI 502691 was significantly activated by Sr²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Zn²⁺and Cu²⁺ tested except for Ca²⁺ which inhibited the enzyme.

Keywords: Glucosidase, chromatography,extract,activity, inhibited